Ask Lemmy

I'm pursuing a PhD in structural engineering and wood science. Here's my perspective on manufactured homes, and why they lack the long-term durability of stick built homes.

The problem with manufactured homes is that they're value-engineered to the point of fragility. A stick built home is built by hand on site. They're built from whatever generic lumber is available from local lumber yards. They're built by imperfect human beings using their own imperfect hands. To compensate for imperfect materials and imperfect human labor, they have a lot of redundancy built in to them. The structure of stick-built homes vary more between each home, so every piece of wood hasn't been optimized down to the absolute minimum. Standardized lumber sizes (2x4, 2x6, 2x8) are used, instead of using custom-milled lumber to produce the absolute minimum cross section for every piece in a home.

But if you're making ten thousand of the same identical manufactured home, you can optimize the hell out of them to make construction as efficient as possible. Instead of imperfect human hands, you use robots to place every piece precisely, and install every fastener perfectly. Instead of using industry-standard lumber sizes, you get lumber mills to custom mill you oddball sizes for particular columns, beams, etc. Instead of buying 2x6s, you get the mill or mill up your own custom "2x5.358." You also do a lot more structural engineering. When you're building ten thousand copies of the same building, it's worth putting in more engineer hours to wring every last pound out of a building's frame. On a normal residential home, it's not worth spending an extra hundred engineering hours just to save a few hundred pounds of wood. But if you're making 10,000 of the same home, those hours can be worth it.

Manufactured homes are, from an engineering point of view, far more efficient than a stick built home. Like airplanes, they have every extra ounce of material optimized out of their design. But as we saw in supply chains during the pandemic, efficiency and resiliency are often inversely correlated. The problem with over-optimization is that it's only ideal as long as the building will never face circumstances beyond what the structural engineer initially estimated. Let's say you design your building to survive a 70 mph wind undamaged. If you have a lot of redundancy, that structure may also be able to withstand an 80 or 90 mph wind undamaged. The over-optimized structure will be a lot more efficient at surviving the 70 mph wind, but if the building ever has to face worse conditions than were assumed during its design....well then you're in trouble.

Finally, stick-built homes will inevitably be far more repairable and upgradeable than factory built homes. Stick build homes are built by actual human hands on site. Factory built homes may be constructed in ways that, while cost effective, are only possible in a factory environment. That which is built on site can be repaired on site. That which is built from mass market generic components can be repaired with mass market generic components. Stick built homes cost more up front, but they inevitably have long-term advantages in terms of resiliency and repairability.